Centre-loaded antenna unit



Sept. 3, 1968 A. J. SPILSBURY CENTRE-LOADED ANTENNA UNIT 3 Sheets-Sheet 1 Filed June 9. 1965 I. 11 IWJ 4174.

zw ll 40 TO rmwsmrrsn Ilvnwrwt ASHTON JAMES SPILSBURY Sept. 3, 1968 A. J. SPILSBURY CENTRE-LOADED ANTENNA UNIT 3 Sheets-Sheet 2 Filed June 1965 mvavm ASHTON JAMES ySPlLSBURY P 1963 A. J. SPILSBURY 3,400,403

CENTRE-LOADED ANTENNA UNIT Filed June 9, 1965 3 Sheets-Sheet 5 nwi/v'rwa ASHTON JAMES SPILSBURY United States Patent 3,400,403 CENTRE-LOADED ANTENNA UNlT Ashton James Spilsbury, 6691 Madrona Crescent, West Vancouver, British Columbia, Canada Filed June 9, 1965, Ser. No. 462,691 Claims. (Cl. 343-750) ABSTRACT OF THE DISCLOSURE A centre-loaded transmitting and receiving antenna having a tubular resonator coil and a single turn inductor band extending around the longitudinal axis of the coil and mounted for adjustment by relative movement between the band and coil, whereby the inductance of the coil can be adjusted by relative movement between the band and coil without contact therebetween, after which the band and coil are releasably secured against further relative movement.

This invention relates to centre-loaded, adjustable radio transmitting and receiving antenna units.

The purpose of a centre-loaded vertical antenna is to increase the effective radiated power from a radio transmitter, by increasing the radio frequency current flowing in the vertical portion of the antenna. This is accomplished by inserting a loading coil, or tuning coil, in the antenna, designing this coil of such a size and with the exact number of turns of wire necessary, to cause the entire antenna system to fall into tune, or resonate at the frequency of transmission. Maximum radiation efficiency of the system is only attained when this coil causes exact resonance of the whole antenna system. Many other factors affect the resonance of the antenna, including height above ground, conductivity of the ground, length of lead wires, and proximity to other metallic systems. To overcome these largely unpredictable elfects it has been customary to use a centre loading coil having fewer turns (less inductance) than necessary and making up the deficiency by introducing artificial inductance in the transmitter itself. However, overall antenna efliciency falls off drastically in proportion to the amount of artificial inductance that is employed at the lower end of the system.

Antennas made in accordance with the present invention are equipped with a centre-loading coil that can be accurately adjusted over a wide range of inductance. This permits the entire antenna system to be resonated to the exact transmitting frequency required without the use of any artificial inductance or other compensations in the radio transmitter itself, thus assuring maximum radiation efiiciency under all circumstances. The range of frequencies that can be covered is further extended by the use of readily interchangeable centre loading coils, any one of which can be tuned over a certain range or band width.

Previous attempts to provide adjustable tuning of antenna coils have involved the use of soldered taps, wiping contacts, contact rollers, contact wheels, and the like. Most of these methods ofier adjustment only in coarse steps, and are subject to contact resistance, contact failure, mechanical breakdown, voltage flashover, and rapid deterioration from dampness, dust, corrosion and weather. These shortcomings are particularly apparent in marine applications.

Two similar types of previously-mentioned centreloaded antennas are illustrated in United States Patent Nos. 2,839,752 and 2,894,260. Both of the patented antennas vary the frequency by (a) sliding the top section of the antenna into the coil to shorten it and reduce top capacity, and (b) using the top section movement to slide a contactor along the inner surface of a coil in order to short out a portion of its inductance to increase the frequency. One uses a toroidal metal spring and the other uses an eight fingered spring as a contact. Neither of these antennas provides accurate fine adjustment. Both antennas have a serious disadvantage of contacting more than one turn of the coil at a time thus forming a shorted turn condition in the coil. The result of this in a transmitting antenna is that excessively high currents develop (eddy currents) in the shorted turn and because of the slider contact, resistance heat is generated, arcing occurs and the contact eventually fails. For this reason, both of these devices can develop trouble, particularly when subject to unfavorable environmental conditions, such as, salt atmosphere, surface corrosion, and the like. Both devices depend on the frequent mechanical adjustments to keep their contacts scraped clean. Neither would remain in a set condition for any length of time without becoming unstable. For these reasons, neither of the patented devices has found any practical application in marine installations, although the antennas have been on the market for a number of years and are used mainly by amateurs.

The main object of the present invention is the provision of centre-loaded antennas which are adapted to withstand unusual mechanical strain from high winds, snow, sleet and salt spray. These antennas are provided with specially designed insulated mounts to facilitate rapid installation and detachment, and they are so constructed that corrosion is kept to a minimum.

Another object is the provision of adjustable tuning antennas which do not have soldered taps, wiping contacts, and the like.

A further object is the provision of a centre-loaded antenna which provides continuous smooth adjustment of the inductance of the coil thereof without the use of wiping contacts and without exposure to flashover, a leakage or arcing of any kind.

Another object is the provision of a centre-loaded antenna that can be tuned over a very wide range of frequencies.

Yet another object is the provision of a centre-loaded antenna that can be used with multi-frequency transmitters and is adapted to resonate correctly for each frequency.

A centre-loaded transmitting and receiving antenna unit according to the present invention includes a outer antenna section and an insulated tubular resonator coil having an end connected to this outer section, said coil extending around a longitudinal central axis. A base antenna section consisting of tube made of aluminum or other suitable material is connected to an opposite end of the coil, and slidably arranged within or surrounding the coil so that the end of the tube forms a single turn inductor band extending around said axis. The relative movement between the band and coil, forms a low resistance inductor variably coupled to the field of the resonator coil. Relative movement between the band and the resonator coil adjusts the inductance of the coil without any contact therebetween. If desired, a plurality of axially spaced inductor bands insulated from each other may be used. These should be spaced apart a distance equal to approximately one half of the diameter of the bands. As the edge of a flat disc inside a resonator coil would act in the same manner as an inductor band, the latter term herein is intended to include such a disc edge.

Examples of this invention are illustrated in the accompanying drawings, in which,

FIGURE 1 is an elevation of one form of antenna embodying this invention,

FIGURE 2 is an enlarged vertical section through this antenna,

FIGURE 3 is a cross section taken on the line 33 of FIGURE 2,

FIGURE 4 is a schematic diagram of this antenna,

FIGURE 5 is a reduced elevation, partly in section, of an alternative form of antenna,

FIGURE 6 diagrammatically illustrates an alternative form of the invention,

FIGURE 7 is an enlarged vertical section through the resonator coil and ring arrangement of the alternative of FIGURE 6,

FIGURE 8 diagrammatically illustrates another use of the unit of FIGURE 6, and

FIGURE 9 is a wire diagram of another alternative form of the invention.

Referring to FIGURES 1 to 4 of the drawings, 10 is a centre-loaded antenna according to this invention, and including a tubular support 12 formed of suitable nonconducting material, such as a phenolic resin. A resonator coil 15 is wound on and carried by this support. In the illustrated example, coil 15 is formed of bare copper wire with 12 turns per inch embedded in a resinous coating 16. This coating may be formed of an epoxy resin. However, instead of winding coil 15 on the outer surface of support 12, said coil may be embedded in the material forming the support.

An outer antenna section is mounted on and projects outwardly from the upper end 22 of support 12. In this example, a plug 23 is fitted in the upper end of support 12, and the lower end of section 20 fits tightly in a bore 25 extending through this plug. The outer antenna section 20 may be of any standard construction. For example, it can be formed with a metal base or male connector 27 which fits in a plug bore 25, a Phosphor bronze wire 29 connected to and extending upwardly from connector 27 and encased in a fibreglass coating 30 which keeps the wire erect and protects it against corrosion. The upper end of coil 15 is connected to a screw 33 which extends through support 12, is threaded through the side of plug 23 and normally is turned in to engage connector 27 of the outer antenna section to form an electrical connection between the coil and said connector which, in turn, is connected to antenna wire 29.

The lower end 36 of support 12 is fitted in a sleeve 38 formed of anodized metal, The lower end of coil 15 is connected by a screw 39 to sleeve 38.

A tubular supporting shaft 40 formed of a conducting material, which may be anodized aluminum, constitutes a base antenna section for the antenna as well as a support for the above-mentioned elements thereof. The upper end of shaft 40 slidably fits within tubular support 12 and is retained in any desired adjusted position relative to said tubular support by a plurality of screws 42 which are threaded through sleeve 38, extend through support 12 and bear against said shaft. These screws not only hold support 12 in position on shaft 40, but they form an electrical connection between said shaft and sleeve 38 which in turn, is connected to coil 15 by screw 39. Shaft 40 is electrically connected to a radio receiver and transmitter in the usual manner.

The upper end of shaft 40 constitutes a single turn inductor band 45 which is movable relative to coil 15 to adjust the inductance thereof. When it is desired to tune antenna 10, screws 42 are loosened, and support 12 is shifted up and down on shaft 40 until the entire antenna system is in tune or resonates at the frequency of transmission. Screws 42 are tightened after each adjustment to provide contact, and the antenna remains in this tuned arrangement until the adjustment is changed. Shaft 40 can be formed of anodized aluminum pipe, while plug 23 and sleeve 38 can be formed of corrosion resistant aluminum castings, and stainless steel screws are used.

If desired, shaft 40 may be made large enough to fit over the outer surface of support 12 and coil 15, in

which case the inductor band would be positioned outside said coil.

FIGURE 4 is a schematic diagram of antenna 10.

Antenna 10 can be readily and accurately tuned to any operating frequency. If a different resonator coil is required, it is only necessary to remove coil 15 and to substitute another coil. When this antenna is tuned, it provides greatly increased radiation efficiency, and the entire antenna system is electrically stable and is not very easily detuned or affected by external causes. The tuning adjustment is continuous, and no high voltages are developed in the tuning mechanism, no leakage paths created, and no electrical contacts are exposed to moisture and corrosion. When tuned to resonance, all of the base antenna section, which may be exposed to personnel, operates at very low voltage and can be touched or handled during transmission without danger.

When maximum efilciency is desired on more than one frequency, two or more antennas 10 can be connected in multiple to a transmitter without the use of a switching device, see FIGURE 5. In this case, each antenna includes a conducting base antenna section in the form of a tubular shaft 40a which is mounted on and projects upwardly from a base 50, said base being carried by a tubular shaft 51 which is electrically connected to the transmitter in the usual way. The resonator coils of antennas 10 are shifted up and down their respective shafts 40a for tuning purposes. The coils of these antennas will be suitable for different frequencies, and for proper operation, these frequencies should differ by at least 10%. The resonator coils and the outer antenna sections thereof must be separated by substantial distances in comparison to the sizes of the antenna. For example, the upper tips of the outer antenna sections can be spaced about 3 feet from each other.

With the arrangement of FIGURE 5, only the antenna 10 which is resonant at the operating frequency of the transmitter will draw appreciable power therefrom, and the other two antennas will remain inactive, Thus, automatic selection of antennas is accomplished with this arrangement.

FIGURES 6 and 7 illustrate an alternative antenna unit 60 used in association with an umbrella antenna indicated at 61. Unit 60 includes a vertical tube or shaft 64 formed of aluminum or other suitable material supported at the top of a tower 65. Shaft 64 is electrically connected by a lead wire 66 to a radio receiver and transmitter, not shown, in the usual manner.

An insulating tube 70 is mounted on the upper end of shaft 64 and extends upwardly therefrom, while a short tube 72 formed of aluminum or other conducting material projects from the upper end of tube 70 and is connected thereto. A conical roof 74 formed of aluminum or other suitable conducting material fits over and is secured to the upper end of tube 72. The wires of antenna 61 are connected to the lower edge of this roof, as shown at 75 in FIGURE 7. A tubular housing 76 is connected to and suspended from roof 74. This housing is formed of suitable weather resistant material, such as fibreglass.

A tubular support 78 formed of insulating material, such as fiberglass, has insulating caps 79 and 80 at its opposite ends slidably mounted on pipe 70. A resonator coil 83 is mounted on the outer surface of support 78 and embedded in a suitable coating material, such as epoxy resin. The upper end of coil 83 is connected by a wire 85 to conducting pipe 72, while the lower end of said coil is connected by a wire 86 to the upper end of tube 64. One or more inductor bands 89 formed of metal are mounted on the outer surface of housing 76 near the upper end thereof where coil 83 can be moved therethrough without coming into contact therewith. If two bands are used, as shown, these should be separated by a distance equal to about one-half of the diameters thereof.

Suitable means is provided for moving coil 83 relative to bands 89. In this example, an adjusting screw 92 is threaded through lower cap 80, and rotatably extends through a bearing 93 connected to and supported by pipe 70 which, in turn, is supported by shaft 64. A pulley 95 is fixedly secured to the lower end of screw 92. A rope or cable 96 extends up from the ground through shaft 64, around pulleys 97 and pulley 95, and back down to the ground again. Thus, screw 92 can be turned by means of cable 96, and this moves coil 83 up or down relative to bands 89.

If desired, a lightning rod 98 may be provided in unit 60, said rod being connected at its upper end to roof 74 while its lower end extends down into the upper end of shaft 64.

FIGURE 8 illustrates antenna unit 60 suspended from ahorizontal antenna 100 extending between towers 101 and 102.

Unit 60 operates in the same manner as the previouslydescribed antenna, excepting that the resonator coil moves within two inductor bands instead of outside of one such band.

An antenna incorporating the present invention can be provided for use with multi-frequency transmitters. In this case, a plurality of inductor bands are used, one for each frequency channel of the transmitter. Each band is connected by wires to a switch across the gap thereof. When a particular frequency is used, the switch of the band for that frequency is closed, thereby completing the band circle, so that it functions in the same manner as the inductor bands described above.

FIGURE 9 diagrammatically illustrates this multiple open band idea. In this example, a plurality of open, single turn inductor bands 108, 109, 110 are provided, said bands being axially spaced and insulated from each other. The open ends of bands 108, 109 and 110 are connected to switches 112, 113 and 114, respectively. A resonator coil 118 is adapted to be moved within and relative to said band.

Bands 108, 109 and 110 are adapted to control different frequencies of a multi-frequency transmitter. When one of the switches is closed, the band electrically connected to that switch is in effect changed to a complete circular band and functions in the manner described above relative to coil 118.

What I claim as my invention is:

1. A center-loaded transmitting and receiving antenna unit comprising an outer antenna section, an insulated tubular resonator coil having an end connected to the outer antenna section, said coil extending around a longitudinal central axis, a base antenna section connected to an opposite end of said coil, said base antenna section being adapted to be connected to a radio transmitter and receiver, a single turn inductor band extending around said axis at the coil and mounted for adjustment by relative movement between the band and coil, said inductor band overlapping said resonator coil, and means for fixing the band and coil in any adjusted and overlapping position relative to each other, said band forming a low resistance inductor variably coupled to the field of the resonator coil, whereby relative movement between said band and coil adjusts the inductance of said coil without any contact therebetween.

2. A centre-loaded transmitting and receiving antenna unit comprising an outer antenna section, an insulated tubular resonator coil having an end connected to the outer antenna section, said coil extending around a longitu-dinal central axis, a base antenna section connected to an opposite end of said coil, said base antenna section being adapted to be connected to a radio transmitter and receiver, and a plurality of axially spaced, single turn inductor bands extending around said axis insulated from each other and from the coil, each of said bands forming a low resistance inductor variably coupled to the field of the resonator coil, said bands being fixed relative to each other and mounted for relative movement between the bands and the coil, whereby relative movement between said bands and the coil adjusts the inductance of said coil without any contact therebetween.

3. A centre-loaded antenna unit for multi-frequency transmitters and receivers, comprising an outer antenna section, an insulated tubular resonator coil having an end connected to the outer antenna section, said coil extending around a longitudinal central axis, a base antenna section connected to an opposite end of said coil, said base antenna section being adapted to be connected to the multi-frequency transmitter, a plurality of axially spaced, single turn open inductor bands extending around said axis insulated from each other and from the coil, a switch connected across the opening of each band and the switch connected thereto forming an inductor circuit, said bands being fixed relative toeach other-and mounted for relative movement between the bands and the coil, whereby relative movement between each band when the switch connected thereto is closed and the coil adjusts the inductance of said coil without any contact therebetween.

4. A centre-loaded antenna unit for transmitters having a plurality of operating frequencies differing from each other by at least 10% and including a plurality of spaced antennas; each antenna comprising an outer antenna section, an insulated tubular resonator coil having an end connected to the outer antenna section, said coil extending around a longitudinal central axis, a base antenna section connected to an opposite end of said coil, and a single turn inductor band extending around said axis at the coil and mounted for relative movement between the band and the coil, said inductor band overlapping said resonator coil, and means for fixing the band and coil in any adjusted and overlapping position relative to each other, said band forming a low resistance inductor variably coupled to the field of the resonator coil; base sections of said antennas being adapted to be connected in multiple to a multi-frequency transmitter and the resonator coils being tuned to the operating frequencies of the transmitters connected to their respective base sections.

5. A centre-loaded transmitting and receiving antenna unit comprising a tubular support formed of non-conducting material, a tubular resonator coil wound on and carried by said support, an outer antenna section secured to and projecting outwardly from an end of the support, means for connecting an adjacent end of the coil to said outer section, a base antenna section in the form of a tubular supporting shaft formed of conducting material slidably fitting in an opposite end of the tubular support, said supporting shaft being adapted to be connected to a radio transmitter and receiver, and means for releasably securing the tubular support on the supporting shaft with an end of said shaft in said coil and securing an opposite end of the coil to said shaft spaced from the end of the latter within the coil, said end of the shaft forming a single turn inductor band within and insulated from the resonator coil and movable relative to said coil to adjust the inductance thereof.

6. A centre-loaded transmitting and receiving antenna unit comprising a tubular support formed of non-conducting material, a tubular resonator coil wound on and carried by said support, a plug closing an upper end of the support, an outer antenna section mounted in said plug and projecting outwardly from the support, means for connecting an adjacent end of the coil to the outer section in the plug, a sleeve formed of conducting material fitted on a lower end of the support, means for connecting an opposite end of the coil to said sleeve, a base antenna section in the form of a tubular supporting shaft formed of conducting material slidably fitting in said lower end of the support, said supporting shaft being adapted to be connected to a radio transmitter and receiver, means for releasably securing the tubular support on the supporting shaft with an end of said shaft in said coil and electrically connecting the sleeve to said shaft, the end of the shaft within the coil forming a single turn inductor band within and insulated from the resonator coil and movable relative to said coil to adjust the inductance thereof.

7. A centre-loaded transmitting and receiving antenna unit comprising a tubular support formed of non-conducting material, a tubular resonator coil wound on and carried by said support, a housing formed of non-conducting material surrounding and spaced from said coil, said housing and said coil being movable axially one relative to the other, said coil being adapted to be electrically connected at one end to an antenna and at an opposite end to a radio transmitter and receiver, and at least one single turn inductor band carried by the housing and extending around the coil, said band forming a low resistance inductor variably coupled to the field of the resonator coil, whereby relative movement between said band and coil adjusts the inductance of said coil without any contact therebetween.

8. A centre-loaded transmitting and receiving antenna unit comprising a tubular support formed of non-conducting material, a tubular resonator coil wound on and carried by said support, a housing formed of non-conducting material surrounding and spaced from said coil, said housing and said coil being movable axially one relative to the other, said coil being adapted to be electrically connected at one end to an antenna and at an opposite end to a radio transmitter and receiver, and a plurality of single turn, axially spaced inductor bands insulated from each other and carried by the housing and extending around the coil, each of said bands forming a low resistance inductor variably coupled to the field of the resonator coil, whereby relative movement between said bands and the coil adjusts the inductance of said coil without any contact therebetween.

9. A centre-loaded transmitting and receiving antenna unit comprising a tubular support formed of non-conducting material, a tubular resonator coil wound on and carried by said support, a housing formed of non-conducting material surrounding and spaced from said coil, said housing and said coil being movable axially one relative to the other, said coil being adapted to be electrically connected at one end to an antenna and at an opposite end to a radio transmitter and receiver, at least one single turn inductor band carried by the housing and extending around the coil, means connected to but insulated from the coil and the band for causing relative movement therebetween, said band forming a low resistance inductor variably coupled to the field of the resonator coil, whereby relative movement between said band and coil adjusts the inductance of said coil without any contact therebetween.

10. A centre-loaded transmitting and receiving antenna unit comprising a tubular support formed of non-conducting material, a tubular resonator coil wound on and carried by said support, a housing formed of non-conducting material surrounding and spaced from said coil, said housing and said coil being movable axially one relative to the other, a roof on the housing formed of conducting material and adapted to be connected to an antenna, means electrically connecting an end of the coil to said roof, an opposite end of said coil being adapted to be connected to a radio transmitter and receiver, and at least one single turn inductor band carried by the housing and extending around the coil, said band forming a low resistance inductor variably coupled to the field of the resonator coil, whereby relative movement between said band and coil adjusts the inductance of said coil without any contact therebetween.

References Cited UNITED STATES PATENTS 2,103,646 12/1937 Schlesinger 343750 2,841,789 7/1958 Bassett 343749 2,993,204 7/1961 Macalpine 343750 3,104,394 9/1963 Yokoyama 343-750 3,172,109 3/1965 Senrui 343-749 3,264,647 8/ 1966 Nuttle 343-75O ELI LIEBERMAN, Primary Examiner. 

